In the field of printing, the most common type of printer has been the printer which impacts against record media that is caused to be moved past a printing line or line of printing. As is well-known, the impact printing operation depends upon the movement of impact members, such as print hammers or wires or the like, which are typically moved by means of an electromechanical system and which system enables precise control of the impact members.
In the field of dot matrix printers, it has been quite common to provide a print head which has included therein a plurality of print wire actuators or solenoids arranged or grouped in a manner to drive the respective print wires a very short, precise distance from a rest or non-printing position to an impact or printing position. The print wires are generally either secured to or engaged by the solenoid plunger or armature which is caused to be moved such precise distance when the solenoid coil is energized and wherein the plunger normally operates against the action of a return spring.
In the wire matrix printer, the print head structure may be a multiple-element type with the wire elements aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in line manner, while the drive elements or transducers may be positioned in a circular configuration with the respective wires leading to the front tip of the print head.
Alternatively, the printer structure may include a plurality of equally-spaced, horizontally-aligned single-element print heads which are caused to be moved in back-and-forth manner to print successive lines of dots in making up the lines of characters. In this latter arrangement, the drive elements or transducers are individually supported along a line of printing. These single wire actuators or solenoids are generally tubular or cylindrically shaped and include a shell which encloses a coil, an armature and a resilient member arranged in manner and form wherein the actuator is operable to cause the print wire to be axially moved a small precise distance in dot matrix printing. The print wire is contained and guided at the front of the solenoid in axial direction during the printing operation. It is with the field of print wire actuators that the subject matter of the present invention is most closely associated and which provides for improved positioning and control of the print wire during printing operations.
While the conventional actuator of the type utilizing magnetic energy, such as the solenoid, is widely used, its low electro-mechanical conversion efficiency is a disadvantage when compared with a piezoelectric crystal element actuator utilizing the piezoelectric effect which permits a highly efficient electro-mechanical conversion.
Representative documentation in the field of dot matrix print head wire actuators includes U.S. Pat. No. 3,831,729, issued to R. Howard on Aug. 27, 1974, which discloses a solenoid for actuating a print wire normally biased against the impact direction by spiral spring means which experiences a substantially linear spring force upon deflection.
U.S. Pat. No. 3,994,382, issued to R. A. McIntosh on Nov. 30, 1976, discloses a solenoid armature and a print wire wherein the armature is initially driven against an initially weak spring biasing force of a large beam radius spring and prior to the print wire striking the paper, the non-prior linear spring exerts a greater spring force upon the armature to limit the impact velocity and to return at a more rapid rate.
U.S. Pat. No. 4,034,841, issued to S. Ohyama et al. on July 12, 1977, discloses a print wire solenoid including a disc type plunger-restoring spring which has an annular portion and spoke portions which extend inwardly to define a central opening for the plunger. The disc spring is not fixed to the plunger and is free from any stress concentration in operation.
U.S. Pat. No. 4,046,244, issued to J. F. Velazquez on Sept. 6, 1977, discloses a solenoid having an armature with a disc type spring surrounding the armature and contained by and between a pair of plastic annular washers, one of the washers being formed to allow the spring to flex in conical manner.
U.S. Pat. No. 4,176,976, issued to J. Lendl on Dec. 4, 1979, discloses a print head with print wires driven by flexural bending elements in the form of piezoelectric strips or diaphragm pieces which are supported by bearings located at nodal oscillation points of the elements.
U.S. Pat. No. 4,193,703, issued to W. Sakmann on Mar. 18, 1980, discloses a printer with a piezoelectrically driven printing needle wherein expansion of the piezo element is transferred as a change in length to a buckling spring attached to the printing needle.
U.S. Pat. No. 4,272,200, issued to W. H. Hehl on June 9, 1981, discloses a piezoelectric driven matrix printer in the shape of a horn tapered in the direction of printing elements and having a base to which is attached a piezoelectric crystal excitation device.
U.S. Pat. No. 4,523,866, issued to P. Hirzinger et al. on June 18, 1985, discloses a wire print head having piezoelectric drive elements in the form of strips which are bonded to flexible tabs directed radially inward from a support ring. The ring is secured between a wire guide structure and a cover, and the drive ends of the print wires supported in the wire guide structure are directly driven by the ends of the flexible tabs.
And, U.S. Pat. No. 4,523,867, issued to H. R. Berrey et al. on June 18, 1985, discloses a bi-directional drive actuator with forward velocity and reverse position closed loop feedback control wherein a forward input power pulse can be varied as to magnitude and duration for desired forward velocity of the print wire, and a reverse input power pulse can be modulated for magnitude and duration for desired rearward velocity of the wire.
Further, the principle of using a multilayeed type actuator is disclosed in the Institute of Electronics and Communication Engineers of Japan Technical Report, Vol. 84, No. 289, EMC 84-49, issued on Feb. 15, 1985.